The research site is a planted
sweetgum (Liquidambar styraciflua) monoculture located on the Oak
Ridge National Environmental Research Park (35o 54' N; 84o
20' W) in southeastern United States. Oak Ridge is in eastern Tennessee
Ridge and Valley province between the Cumberland and Blue Ridge
The plantation was established
in spring, 1988, on an old terrace of the Clinch River (elevation 230 m).
One-year-old, bare-rooted sweetgum seedlings were planted at a spacing
of 2.3 m × 1.2 m. There is a total of 1.7 ha planted with sweetgum
in two areas � a 185 × 70 m area and a smaller 85 × 50 area,
separated by a stand of sycamore (Platanus occidentalis) that was
used in a N nutrition experiment (van Miegroet et al. 1994). No fertilizer
has been added to the sweetgum; herbicide was used in 1989 and 1990 to
control competition from weeds.
When the experiment was
initiated in 1997, stand basal area was 29 m2/ha with an average
tree height of 12.4 m and stem diameter of 11.3 cm. The height and
basal area are very uniform across both areas planted in sweetgum. The
sweetgum stand has a closed canopy with a leaf area index of 5; lower branches
are self-pruning and there is some mortality of suppressed trees.
The understory was very
sparse when the experiment was started in 1997 but has become more aggressive
since then. Important species include an invasive C4 annual grass (Microstegium
vimineum), non-native, invasive woody plants (Lonicera japonica,
Ligustrum sinense), and other taxa. Tree seedlings, including Acer
negundo, Acer rubra, Liriodendron tulipifera, Quercus alba, are sparse.
The soil at the site, which
is classified as Wolftever, an Aquic Hapludult, developed in alluvium washed from
upland soils derived from a variety of rocks including dolomite, sandstone,
and shale. It has a silty clay loam texture and is moderately well
drained (SCS 1967, van Miegroet et al. 1994). The soil is slightly
acid (water pH approximately 5.5-6.0) with high base saturation largely
dominated by exchangeable Ca.
bulk density 1.5 g/cm3
The climate is typical of
the humid southern Appalachian region. Mean annual temperature is 14.2°C
and mean annual precipitation is 1390 mm. Precipitation is generally evenly
distributed throughout the year.
More Oak Ridge climate data are available from the Atmospheric
Turbulence and Diffusion Division
Service. 1967. Soil survey and laboratory data and descriptions for some
soils of Tennessee. Soil Survey Investigations Report No. 15, U.S.
Dept. Agric., Soil Conservation Service and Tennessee Agricultural Experiment
van Miegroet, H., R. J. Norby,
and T. J. Tschaplinski. 1994. Optimum nitrogen fertilization in a short-rotation
sycamore plantation. Forest Ecology and Management 64:25-40.